In the manufacturing process of a semiconductor device, it is required to perform an etching so as to form hole patterns or line patterns with a high aspect ratio in response to the demand for the scaling-down of a design rule. There has been disclosed a technique for such high aspect-ratio etching, e.g., a method for using a mask (multi-layered resist) having a structure where inorganic films and organic films are deposited below an ArF resist. As such a lower organic film, an amorphous carbon layer having a high etching resistance is employed.
Typically, O2 gas is employed as an etching gas when a carbon-based organic film, e.g., an amorphous carbon layer, is etched by using an inorganic film as a mask (see, e.g., Japanese Patent Application Publication No. 2004-214465).
However, when hole patterns or line patterns are formed by etching an amorphous carbon layer with a plasma of O2 gas, such etching is performed in both vertical and horizontal directions, thereby making errors such as bowings in etched shapes or enlarging hole diameters or line widths beyond the designed values. If such errors are made in a specific film, errors are also made in a target film to be etched when the etching is performed on the target film by using the specific film as a mask.
There has been known a method for reducing the generation of the errors by adding COS gas. However, it may be difficult to use the COS gas due to residues made from the COS gas, and the like. Accordingly, it is required to find a method for obtaining satisfactorily etched shapes by using O2 gas only.